Loudspeakers, or speakers, are included in a wide variety of devices. For example, telecommunications devices, such as mobile telephones or smartphones, include speakers for audio communication as well as for video and audio media playback.
In free space, the soundwaves emitted by the different sides of the speaker, such as the front and the back of the speaker, will interact and cause undesired cancellation affects. In order to reduce the undesired cancellation affects, speakers are generally placed within an enclosure that defines a speaker cavity to the rear of the speaker filled with, for example, air.
While placement of the speaker within an enclosure mitigates the undesired cancellation affects, the enclosure and, more particularly, the speaker cavity defined by the enclosure may create other issues. In this regard, the air within the speaker cavity acts as a spring having a stiffness proportional to the volume of the speaker cavity. A small speaker cavity has a high stiffness and will therefore impede the motion of the speaker membrane. The impedance of the speaker membrane reduces the efficiency of the speaker, particularly at low frequencies. While larger speaker cavities do not impede the motion of the speaker membrane to as great of a degree, many devices including telecommunication devices, such as mobile telephones, hands free communication devices and laptop and tablet computers, have only limited space available for the speaker such that the enclosure and the resulting speaker cavity must be relatively small. As a result, the speakers housed by such relatively small enclosures may provide sub-optimal sound quality including, for example, the “tinny” sound provided by some speakers disposed within small enclosures.
The challenges associated with the dedication of a sufficient volume within a device for a speaker cavity may be further complicated by the electronic components that are also included within the device, such as a telecommunications device, that includes a speaker. At least some of the components, such as central processing units, graphical processing units, optical modules or the like, have a relatively large heat flux and therefore generate substantial heat while in use. In order remove the heat and ensure that the components remain at a temperature that permits the components to operate properly, conductive or multiphase thermal paths may be provided between the components that serve as the sources of heat and the surrounding environment. However, these thermal paths also have volumetric requirements and restrictions in terms of their proximity to other components that are temperature-sensitive.
Thus, the allocation of the volume within a device, such as a telecommunications device, that includes a speaker must take into account a number of competing considerations including the size of the speaker cavity and the necessity for thermal paths to dissipate heat generated by various components of the device. This design challenge has generally increased over time as improvements in the performance of the devices has typically led to an increase in the heat flux generated by the components of the device that must be dissipated. Moreover, the desire for further miniaturization of the devices, such as telecommunications devices, has imposed increasingly stringent restrictions on the volume available for heat dissipation, speaker cavities and the like.
In an effort to improve the performance of speakers, alternative enclosures for speakers have been considered. For example, ported enclosures have been designed that define a small vent attached to a relatively short waveguide. The vent changes the acoustic characteristics of the enclosure from a sealed box to a Helmholtz resonator. The air inside the relatively small waveguide and the speaker cavity acts as a mass-spring system, which has a different reactance than that provided by a sealed speaker cavity. This change in reactance can lead to enhanced speaker efficiency at low frequencies. Similarly, transmission line enclosures, quarter wavelength enclosures and passive radiators have been developed that also change the acoustic performance of a speaker. Further, enclosures have been designed in which the volume provided by the speaker cavity is filled with a material to lower the characteristic speed of sound within the speaker cavity, thereby increasing the effective volume of the speaker enclosure and reducing the impedance to the speaker motion. However, these alternative enclosure designs have increased complexity and, as a result, may be more challenging and expensive to manufacture, particularly for small devices.